Numerous environmental and industrial chemicals alter male reproductive function. One of the most sensitive tests in laboratory animals involves serial histopathology. We are coupling this approach with serial sperm analyses to evaluate how boric acid affects the male reproductive system in rats. In addition, we are evaluating the rabbit as a model for human reproductive toxicity. The rabbit is uniquely suited, as it is the only common non-primate lab species which shares with humans the ability to produce serial semen samples. Thus, this project is evaluating changes in rabbit seminai parameters (sperm endpoints, seminal biochemistry, pH, osmolality, etc.) after exposure to ethylene dibromide, a compound previously shown to affect human seminal endpoints. A critical addition to this project will be a test assessing the fertilizing capability of a constant number of spermatozoa from treated and control animals. Significance: These studies continue our characterization of testicular lesion development, identify the most sensitive cell to boric acid, and evaluate the rabbit as a model for human reproductive hazard.